Resin curing is a process in which thermosetting resins undergo irreversible changes through chemical reactions such as condensation, ring closure, addition or catalysis, and curing is completed by adding curing (crosslinking) agents. Curing agent is an essential additive. Whether it is used as adhesive, coating or castable, curing agent needs to be added, otherwise epoxy resin cannot be cured. The types of curing agents have great influence on the mechanical properties, heat resistance, water resistance and corrosion resistance of cured products.
2. The proportion of curing agent should be determined by calculation.
Calculation method of curing agent dosage:
When (1) amine is used as crosslinking agent, its calculation is as follows:
Amine dose =MG/Hn
Where: M= molecular weight of amine; Hn= number of active hydrogen; ; G= epoxy value (number of epoxy equivalents contained in epoxy resin per 100g)
(2) When using anhydride as crosslinking agent, press the following formula:
Anhydride dosage = mg (0.6 ~1)100.
Where: M= molecular weight of anhydride; G= epoxy value (0.6~ 1) is the experimental coefficient.
Extended data:
Classification of curing agents
Curing agents can be divided into normal temperature curing agents and heating curing agents according to their uses. Generally, epoxy resin has excellent curing performance at high temperature, but the coatings and adhesives used in civil buildings need to be cured at room temperature because of the difficulty in heating, so most of them use aliphatic amines, alicyclic epoxy resins and polyamides, especially in winter, and they have to be used together with polyisocyanates or odorous polyols.
As for the medium-temperature curing agent and high-temperature curing agent, they should be selected according to the heat resistance of the adherend and the heat resistance, adhesiveness and drug resistance of the cured product. Selection focuses on polyamines and anhydrides. The cured anhydride has excellent electrical properties, so it is widely used in electronics, electrical appliances and other fields.
The cured aliphatic polyamine has good adhesion, alkali resistance and water resistance. Aromatic polyamines also have excellent drug resistance. Because the nitrogen element of amino group forms hydrogen bond with metal, it has excellent antirust effect. The higher the mass concentration of amine, the better the antirust effect. Anhydride curing agent forms ester bond with epoxy resin, showing high resistance to organic acids and inorganic acids, and its electrical properties generally exceed those of polyamines.
References:
Baidu encyclopedia-curing agent
Baidu encyclopedia-epoxy resin